1. Field of the Invention
The present invention relates to a belt device capable of correcting a meandering of a belt, such as an intermediate transfer belt, a conveying belt, or a photosensitive element belt, and an image forming apparatus including the belt device.
2. Description of the Related Art
Among image forming apparatuses, such as a copier, a printer, a facsimile machine, and a multifunction product (MFP), a tandem-type color image forming apparatus including an intermediate transfer belt (for example, as disclosed in Japanese Patent Application Laid-open No. 2006-343629 and Japanese Patent Application Laid-open No. 2001-83840) has been commonly used.
In such a tandem-type color image forming apparatus, four photosensitive drums as image carriers are tandemly arranged to be opposed to an intermediate transfer belt. The image forming apparatus forms a full-color image in such a manner that black (K), yellow (Y), magenta (M), and cyan (C) toner images are formed on the photosensitive drums, respectively. The K, Y, M, and C toner images formed on the photosensitive drums are sequentially transferred onto the intermediate transfer belt in a superimposed manner. The superimposed toner image transferred onto the intermediate transfer belt is further transferred onto a recording medium, and thereby forming a full-color image.
Various technologies have developed to improve such an image forming apparatus. For example, an image forming apparatus as disclosed in Japanese Patent Application Laid-open No. 2006-343629 and Japanese Patent Application Laid-open No. 2001-83840 is configured to detect a displacement of an intermediate transfer belt in a width direction. Therefore, the image forming apparatus can correct a meandering of the intermediate transfer belt (the displacement in the width direction) based on a result of the detection.
Specifically, in the image forming apparatus disclosed in Japanese Patent Application Laid-open No. 2006-343629, a displacement sensor detects an amount of displacement of a contact that is in contact with an edge portion of the intermediate transfer belt (an endless belt). When the intermediate transfer belt meanders, the contact oscillates along with the meandering of the intermediate transfer belt, so that the meandering of the intermediate transfer belt can be detected based on a result of the detection by the displacement sensor. The meandering of the intermediate transfer belt is corrected by a meandering correction roller, which is one of rollers supporting the intermediate transfer belt, based on the amount of the displacement of the contact. More specifically, an oscillating arm connected to the meandering correction roller is moved by a movement of an eccentric cam to change the tilt of a rotating shaft of the meandering correction roller, and thereby correcting the meandering of the intermediate transfer belt.
Furthermore, in a belt device disclosed in Japanese Patent No. 3082452, a meandering of a conveying belt (a transfer-medium conveying belt) is corrected in such a manner that a supporting arm connected to a tension applying roller, which is one of rollers supporting the conveying belt, is moved by a movement of a cam to change the tilt of a rotating shaft of the tension applying roller.
Moreover, in a belt device disclosed in Japanese Patent Application Laid-open No. H10-152242, an alignment of a steering roller for correcting a meandering of an endless belt can be manually adjusted.
However, the above conventional technologies have problems. For example, in the image forming apparatus disclosed in Japanese Patent Application Laid-open No. 2006-343629, there are such problems that the apparatus is caused to stop operation because it is determined that a control error occurs when a meandering of the intermediate transfer belt is not corrected within a predetermined time; and a meandering of the intermediate transfer belt cannot be sufficiently corrected within a travel range of the meandering correction roller, i.e., the meandering correction roller cannot be moved enough to correct the meandering of the intermediate transfer belt because of the limitation of the travel range. Such problems are caused, for example, because a plurality of roller members supporting the intermediate transfer belt is installed in the belt device in a state where the parallelism of the roller members is not sufficiently maintained, a frame that rotatably supports the roller members is distorted, or the straightness of the roller members is not sufficiently maintained, so that a default position of the meandering correction roller is significantly deviated in either a forward direction or a backward direction away from a center position of the travel range.
To solve the problems, an assembly accuracy of components of the belt device, such as the roller members and the frame, and an accuracy of each of the components need to be improved. However, in this case, there is a production limitation costwise.
These problems are especially prominent in a case where the apparatus is large in size because a length of the roller members in a direction of the rotating shaft gets longer.
Incidentally, the above problems are not limited to a belt device employing an intermediate transfer belt as a belt member, but are common issues among belt devices that correct a meandering of a belt member regardless of a type of the belt member.